Process for preparing alpha-olefin polymers

ABSTRACT

Alpha-olefin polymerization catalysts are prepared by heating a solid porous carrier having reactive OH groups in the atmosphere of an oxygen-containing gas. The resulting catalysts exhibit higher productivity and produce ethylene polymers or ethylene/C3-C10 copolymers having higher bulk density than similar catalysts prepared with the carriers heated in an atmosphere of nitrogen.

This is a divisional of copending application Ser. No. 657,642, filed onOct. 4, 1984 and now U.S. Pat. No. 4,562,169.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for polymerizing alpha-olefins, acatalyst for such a polymerization method and a method for producingsuch a catalyst. More particularly, the invention relates to a catalystand to a method of using thereof in alpha-olefin polymerizationreactions which produces linear low density polyethylene (LLDPE) andhigh density polyethylene (HDPE) having high bulk density. The inventionalso relates to a catalyst composition exhibiting very high productivitycharacteristics, as compared to similar prior art catalysts.

2. Description of the Prior Art

Linear low density polyethylene polymers possess properties whichdistinguish them from other polyethylene polymers, such as homopolymersof polyethylene. Certain of these properties are described in Andersonet al., U.S. Pat. No. 4,076,698.

Karol et al., U.S. Pat. No. 4,302,566, describes a process for producingcertain linear low density polyethylene polymers in a gas phase, fluidbed reactor.

Graff, U.S. Pat. No. 4,173,547, Stevens et al., U.S. Pat. No. 3,787,384,Strobel et al., U.S. Pat. No. 4,148,754, and Ziegler, deceased, et al.,U.S. Pat. No. 4,063,009, each describe various polymerization processessuitable for producing forms of polyethylene other than linear lowdensity polyethylene, per se.

Graff, U.S. Pat. No. 4,173,547, describes a supported catalyst obtainedby treating a support with both an organoaluminum compound and anorganomagnesium compound followed by contacting this treated supportwith a tetravalent titanium compound.

Stevens et al., U.S. Pat. No. 3,787,384, and Strobel et al., U.S. Pat.No. 4,148,754, describe catalysts prepared by first reacting a support(e.g., silica containing reactive hydroxyl groups) with anorganomagnesium compound (e.g., a Grignard reagent) and then combiningthis reacted support with a tetravalent titanium compound. According tothe teachings of both of these patents, no unreacted organomagnesiumcompound appears to be present when the reacted support is contactedwith the tetravalent titanium compound.

Ziegler, deceased, et al., U.S. Pat. No. 4,063,009, describe a catalystwhich is the reaction product of an organomagnesium compound (e.g., analkylmagnesium halide) with a tetravalent titanium compound The reactionof the organomagnesium compound with the tetravalent titanium compoundtakes place in the absence of a support material.

A vanadium-containing catalyst, used in conjunction withtriisobutylaluminum as a co-catalyst, is disclosed by W. L. Carrick etal in Journal of American Chemical Society, Volume 82, page 1502 (1960)and Volume 83, page 2654 (1961).

Nowlin et al., U.S. patent application Ser. No. 444,152, filed Nov. 24,1982, now U.S. Pat. No. 4,481,301 teach an alpha-olefin polymerizationcatalyst prepared by heating a solid, porous carrier in a nitrogenatmosphere at a temperature of about 100° C. to about 800° C.,contacting the carrier containing reactive hydroxyl groups (OH) with agreater than a stoichiometric amount of an organomagnesium composition,and reacting the product of that step with a tetravalent titaniumcompound, also used in the amount greater than the stoichiometric amountthereof with respect to the hydroxyl groups on the carrier, to produce acatalyst precursor. The catalyst precursor is then combined with anactivator, also known as a co-catalyst, to produce an active catalystcomposition.

It is a primary object of the present invention to provide an activecatalyst composition which is capable of polymerizing alpha-olefinseither in a continuous, gas phase fluid bed process or in a batchreactor process to produce polymers having increased bulk density, ascompared to polymers prepared with the catalysts of prior art.

It is an additional object of the invention to provide an alpha-olefinpolymerization catalyst composition having higher productivity than thecatalysts of prior art.

Additional objects of the invention will become apparent to thoseskilled in the art from the following description of the invention.

SUMMARY OF THE INVENTION

The invention is directed to an improvement in a catalyst compositionand to the use thereof in alpha-olefin polymerization reactions. Thecatalyst composition is prepared in a process comprising the steps of:

(i) heating a solid, porous carrier;

(ii) contacting a solid, porous carrier having reactive OH groups with afirst liquid containing at least one organomagnesium composition havingthe empirical formula

    R.sub.n MgR'.sub.(2-n)                                     (I)

where R and R' are the same or different and they are C₁ -C₁₂hydrocarbyl groups, provided that R' may also be halogen, and n is 0, 1or 2, the number of moles of said organomagnesium composition being inexcess of the number of moles of the OH groups on the carrier;

(iii) removing the first liquid from step (ii) to obtain amagnesium-containing carrier in the form of a dry, free-flowing powder;and

(iv) contacting the powder of step (iii) with a solution comprising asecond liquid and at least one transition metal compound which issoluble in the second liquid.

The magnesium-containing carrier is substantially insoluble in thesecond liquid. As a result, a compound of the transition metal which isinsoluble in the second liquid becomes incorporated onto the carrier,thereby forming a catalyst precursor. The precursor is then combinedwith a sufficient amount of a catalyst activator to obtain acatalytically active catalyst composition.

The improvement of this invention comprises heating the solid, porouscarrier in step (i) at a temperature of about 100° C. to about 1000° C.in an atmosphere of an oxygen-containing gas, rather than in nitrogen,commonly thought equivalent in prior art to the oxygen-containing gas.The resulting catalyst composition exhibits improved productivitycharacteristics, when it is used in a process for polymerizingalpha-olefins, described below, as compared to a similar catalystcomposition wherein the solid, porous carrier is heated in a nitrogenatmosphere.

The present invention also relates to a polymerization process forpreparing a polymer of ethylene or a copolymer of ethylene and one ormore comonomers of C₃ -C₁₀ alpha-olefins, the copolymer containing atleast about 80 percent by weight of ethylene units. The polymerizationprocess is conducted in the presence of the catalyst prepared by theprocess comprising the steps set forth above. The polymerization processsurprisingly produces polymers having increased bulk density as comparedto polymers prepared with catalysts wherein the solid porous carrier isheated in a nitrogen atmosphere.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic illustration of a fluid bed process forproducing polyethylene, such as linear low density polyethylene (LLDPE).

DETAILED DESCRIPTION OF THE INVENTION

The oxygen-containing gas used in step (i) of the process of preparingthe catalyst is any gas comprising oxygen but substantially free ofwater vapor (H₂ O).

Thus, the gas may contain not more than 50 ppm, preferably not more than5 ppm and most preferably not more than 0.5 ppm by volume of such watervapor. The gas comprises at least 1%, usually about 10% to about 100%,preferably about 15% to about 50% by volume of oxygen. In the mostpreferred embodiment, the gas is amoient air which usually comprisesabout 21% by volume of oxygen. The gas is heated to the desiredtemperature and the solid porous carrier is then contacted with theheated gas. The manner of contacting the porous carrier with the heatedgas or the apparatus in which such contact takes place are not crucialto this invention. The carrier can be contacted with the gas in anyconventionally-used apparatus. In the embodiment that is most preferredbecause it is most convenient and requires the least amount ofmodifications from the prior art techniques, the carrier is contactedwith the heated gas, most preferably air, in a fluidized bed reactor.

The length of time that the carrier is in contact with the heated gas(residence time of the carrier in the gas-carrier contact apparatus) isalso conventional for this type of catalyst. The residence time is suchthat it is sufficient to obtain a solid porous carrier containing adesired amount of active OH groups, as specified below.

As the experimental data discussed in detail below indicates, thesubstitution of an oxygen-containing gas for a substantially purenitrogen gas used in prior art to heat the solid, porous carrier,unexpectedly produces a catalyst exhibiting at least about 25%improvement in productivity (defined as grams of polymer produced pergram of catalyst in a gas-phase reactor). The modified carrier heatingprocedure also unexpectedly produces a polymer product whose bulkdensity, defined as mass of granular polymer per unit volume, is atleast about 5%, and usually about 11%, higher than that of polymersprepared with similar catalysts prepared in an identical manner exceptfor the step of heating the solid, porous carrier in a substantiallypure nitrogen atmosphere. These two unexpected and surprising advantagessubstantially lower the overall cost of the polymer product.

The aforementioned advantages, and the magnitude thereof, obtained bysubstituting an oxygen-containing gas for nitrogen in the heating stepof the catalyst synthesis process of this invention are unexpected andsurprising, especially because it was heretofore thought that heatingthe carrier in an oxygen-containing gas is equivalent to heating it in anitrogen atmosphere.

As used herein, the concept of incorporating a material onto a carrierin the catalyst synthesis process is intended to encompass theincorporation of the material (e.g., magnesium compositions andtransition metal compounds) onto the carrier by physical or chemicalmeans. Accordingly, the incorporated material need not necessarily bechemically bound to the carrier.

Catalysts produced according to the present invention are describedbelow in terms of the manner in which they are made.

Suitable carrier materials wnich may be used herein include solid,porous carrier materials, such as silica, alumina and combinationsthereof, which contain reactive OH groups. A suitable carrier is amaterial which, when it is contacted with the first liquid containingthe organomagnesium composition, contains water as represented by thehydroxyl (OH) groups in the amount of about 0.1 mmoles or more of OHgroups per gram of carrier, preferably about 0.1 to about 2.0 mmoles ofOH groups per gram of carrier, and most preferably about 0.3 to about0.5 mmoles of OH groups per gram of carrier. Such carrier materials maybe amorphous or crystalline in form.

Examples of suitable carrier materials are described in Graff, U.S. Pat.No. 4,173,547, the entire contents of which are incorporated herein byreference. Internal porosity of carriers can be determined by atechnique termed BET-technique, described by S. Brunauer, P. Emmett andE. Teller in Journal of the American Chemical Society, 60, pp. 209-319(1938). Specific surface areas of carriers can also be measured inaccordance with the aforementioned BET-technique, with the use of thestandardized method, as descrioed in British Standards BS 4359, Volume1, (1969).

Further examples of suitable carrier materials are given in Stevens etal., U.S. Pat. No. 3,718,636, the entire contents of which areincorporated herein by reference. Polymeric silicas, known aspolysiloxanes, can also be used as suitable carrier materials.

The carrier materials may be in the form of particles having a particlesize of from about 0.1 micron to about 200 microns, more preferably fromabout 10 to about 150 microns. Preferably, the carrier is in the form ofspherical particles, e.g., spray dried silica. The internal porosity ofthe carriers is larger than 0.2 cm³ /gr, preferably larger than about0.6 cm³ /gr. The specific surface area of the carriers is larger thanabout 50 m² /gr, preferaoly from about 150 to about 1500 m² /gr. In themost preferred embodiment, the carrier is silica which has beendehydrated by fluidizing it with air and heating at about 800° C. forabout 8 to 10 hours to achieve a surface hydroxyl group concentration ofabout 0.4 mmols/gr. The silica of the most preferred embodiment is ahigh surface area, amorphous silica (surface area at about 330 m² /gr;pore volume of about 1.50 m³ per gram), and it is a material marketedunder the tradename of Davison 955 by the Davison Chemical Division ofW. R. Grace and Company. The silica is in the form of sphericalparticles, e.g., as obtained by a spray-drying process.

It is desirable to remove physically bound water from the carriermaterial prior to contacting the material with water-reactive magnesiumcompounds. The water removal step may be accomplished by heating thecarrier material in an oxygen-containing gas to a temperature of fromabout 100° C. to an upper limit of temperature represented by thetemperature at which a change of state or sintering occurs. A suitablerange of temperatures is, from about 100° C. to about 1000° C.,preferably from about 150° C. to about 850° C., yet more preferably fromabout 750° C. to about 850° C. and most preferably about 800° C.

Chemically bound water, e.g., as represented by the presence of the OHgroups on the carrier, may be present when the carrier is contacted withwater-reactive organomagnesium compounds in accordance with the presentinvention. Excess OH groups present in the carrier may be removed byheating the carrier, prior to the contacting step, for a sufficient timeat a sufficient temperature to accomplish the desired degree of the OHgroups removal. For example, a relatively small number of OH groups maybe removed by sufficient heating at from about 150° C. to about 250° C.,whereas a relatively large number of OH groups may be removed bysufficient heating at at least 500° or 600° C., preferably from about750° C. to about 850° C. The heating is continued for about 4 to about16 hours. The amount of the hydroxyl groups in silica may be determinedaccording to the method disclosed by J. B. Peri and A. L. Hensley, Jr.,in J. Phys. Chem., 72 (8), 2926 (1968), the entire contents of which areincorporated herein by reference.

While heating is the most preferred means of removing the OH groupsinherently present in many carriers, such as silica, the OH groups mayalso be removed by other removal means, such as chemical means. Forexample, a desired proportion of OH groups may be reacted with asuitable chemical agent, such as a hydroxyl reactive aluminum compound,e.g., triethylaluminum.

A dehydrated carrier material is treated with a solution of a solidorganomagnesium composition in a first liquid, the organomagnesiumcomposition being capable of reacting with a transition metal compound.The organomagnesium composition has the formula R_(n) MgR'.sub.(2-n),where R and R' are the same or different and they are C₁ -C₁₂hydrocarbyl groups, preferably C₁ -C₄ alkane groups, and yet morepreferably C₂ -C₄ alkane groups, provided that R' may also be halogen,preferably bromine or chlorine, and most preferably chlorine, and n is0, 1 or 2. In a preferred embodiment, a solution of such anorganomagnesium composition is a Grignard reagent and the carriermaterial is contacted with the solution thereof in the absence of ballmilling.

Grignard reagents are described in Organic Chemistry, Second Edition,Morrison and Boyd, Second Edition, fifth printing, May 1968, pp. 112-114and 516-521, the entire contents of which are incorporated herein byreference. Grignard reagents are known to react with organic moleculesor moieties which have hydrogen bonded directly to a nitrogen or oxygenatom. Furthermore, Grignard reagents are also known to react withorganic molecules or moieties containing carbonyl groups, cyano groupsand nitro groups. Accordingly, the groups defined by R in theabove-mentioned formula generally should not be any of theaforementioned groups indicated as being reactive with Grignardreagents. Examples of R and R' include C₁ -C₁₂ hydrocarbyl groups (e.g.,C₁ -C₁₂ alkyl or C₆ -C₁₂ aryl) or C₁ -C₁₂ alkoxy groups, which may beunsubstituted or substituted, e.g., with one or more halogens (e.g , F,Cl, Br or I) or with C₁ -C₁₂ alkoxy groups. In the most preferredembodiment, ethylmagnesium chloride is the compound represented by theformula R_(n) MgR'.sub.(2-n).

It is noted that even a Grignard reagent of ethylmagnesium chloride maycontain a mixture of molecules other than ethylmagnesium chloride, perse. For example, particularly under the influence of various liquids orsolvent systems, ethylmagnesium chloride may disproportionate to formsubstantially a mixture of magnesium dichloride and diethylmagnesium.Such mixtures are intended to be encompassed by the formula R_(n)MgR'.sub.(2-n). Accordingly, it will be understood that compositions ofthe formula R_(n) MgR'.sub.(2-n) are intended herein to represent theoverall empirical formula of these compositions rather than to set forththe molecular formula thereof.

Preferably, the carrier is treated with the aforementioned solution insuch a manner that, after the treatment is completed, the carrier hasmagnesium incorporated into the pores thereof. A preferred means ofaccomplishing this result is oy adding a porous carrier to a firstliquid containing a dissolved organomagnesium composition of the formulaR_(n) MgR'.sub.(2-n) and maintaining it in the suspension for about 0.1to aoout 10, preferably about 0.5 to about 5, and most preferably forabout 1.0 to about 2.0 hours (hrs) at a temperature of about 25° C. toabout 200° C., preferably about 50° C. to about 100° C., and mostpreferably about 60° C. to about 80° C. As a result of this treatment,magnesium becomes incorporated into the pores of the carrier by (1) achemical reaction of the organomagnesium composition with the carrier,by (2) a precipitation of magnesium from the organomagnesium compositiononto the carrier or by (3) a combination of such a reaction andprecipitation.

Organomagnesium compositions corresponding to those found in Grignardreagents have the formula RMgX, where R is as defined hereinabove and Xis halogen (e.g., Cl, Br or I), and they are soluble in ethers. Suitableethers are known in the art, e.g., see Yamaguchi et al, U.S. Pat. No.3,989,881, column 4, lines 32-49, the entire contents of this patentbeing incorporated herein by reference, and they include aliphaticethers, such as diethyl ether, diisopropyl ether, dibutyl ether,dipentyl ether and ethyl-n-butyl ether; and cyclic ethers, such astetrahydrofuran and dioxane. Without wishing to be bound by any theoryof operability, it is thought that the reason for the ability of suchethers (e.g., diethyl ether) to solubilize the Grignard reagents (e.g.,C₂ H₅ MgCl) is by virtue of the ability of the magnesium atom to act asa Lewis acid and to associate with at least one electron pair from theetheric oxygen which acts as a Lewis base. Such an association isrepresented as follows: ##STR1##

Thus, the first liquid containing the organomagnesium composition isusually an ether, preferably tetrahydrofuran. Although organomagnesiumcompounds of the formula RMgX tend to be insoluble in non-Lewis basesolvents, such as hexane, they may be completely soluble in mixedsolvent systems, such as hexane/tetrahydrofuran, provided that asufficient solubilizing amount of the Lewis base solvent is present.Thus, a carrier may be slurried in a non-Lewis base co-solvent and anorganomagnesium compound may be added thereto in the form of an ethersolution thereof. Suitable non-Lewis base co-solvents are also known inthe art, see e.g., Graff, U.S. Pat. No. 4,173,547, column 6, line 61 tocolumn 7, line 8. These co-solvents include straight or branchedsaturated aliphatic hydrocarbons, such as butanes, pentanes, hexanes,heptanes, or commonly available mixtures thereof, generally known asgasoline, kerosene, gas, oil or other petroleum fractions. Further, suchco-solvents include cyclic hydrocarbons, such as cyclopentane,cyclohexane, methylcyclohexane, as well as aromatic hydrocarbons, suchas benzene or halogen-aromatic hydrocarbons, such as chlorobenzene. Suchco-solvents should preferably not contain groups which are reactive withthe organomagnesium composition. A preferred co-solvent is n-hexane.

The amounts and concentrations of the organomagnesium/ether solutionwhich is added to the co-solvent/carrier slurry are preferablysufficient to assure that tne organomagnesium composition is at leastpartially soluole in the co-solvent/solvent system. Thus, this amount isdependent upon many factors, such as the composition of solvents, theorganomagnesium composition and the temperature of theco-solvent/solvent system. The selection of proper amounts andconcentrations of organomagnesium/ether solutions is well within theskill of those of ordinary skill in the art. For example, when anethylmagnesium chloride/tetrahydrofuran solution is added to ahexane/carrier slurry, the concentration of the ethylmagnesiumchloride/tetrahydrofuran solution may be from about 0.1 to about 10Molar, preferably from about 1 to about 3 Molar.

For example, when 107 g of silicic acid are suspended in 500 ml ofn-neptane and 342 ml of a solution of 172 mmols of n-propyl magnesiumchloride in diethyl ether are added thereto in accordance with Example 1of Strobel et al, U.S. Pat. No. 4,148,754, the n-propyl magnesiumchloride may well be totally soluble in the n-heptane/diethyl ethermixture. However, when 15 g of silica are slurried in 200 ml of n-hexaneand 50 ml of a 2.0 molar solution of ethylmagnesium chloride intetrahydrofuran is added thereto, the ethylmagnesium chloride appears tobe only partially soluble in the n-hexane/tetrahydrofuran mixture.

A carrier material may also be incorporated with an organomagnesiumcomposition by suitably contacting the carrier material with a liquidcontaining an organomagnesium composition of the formula R_(n)MgR'.sub.(2-n) in a partially dissolved state. More particularly, thecarrier material may be slurried in one of the above-exemplifiednon-Lewis base co-solvents, such as hexane, and a solution of anorganomagnesium composition in a liquid, such as ether, may be addedthereto, the amount of the liquid relative to the amount of co-solventbeing sufficient to only partially solubilize the organomagnesiumcomposition. The non-soluole portion of the organomagnesium compositionmay be in the form of a halomagnesium, e.g., dihalomagnesium, the amountof this non-soluble halomagnesium being essentially equivalent to anamount of dialkylmagnesium remaining soluble in the solvent/co-solventmixture.

It is noted that if the organomagnesium composition is only sparinglysoluble in the liquid, e.g., to the extent of about 1 percent or less,reactive organomagnesium composition which is consumed by reactive siteson the carrier will be replaced by further dissolution of undissolvedorganomagnesium composition by a mass action effect.

Another example of a method of incorporating an organomagnesiumcomposition onto a carrier material is to slurry the carrier material ina Lewis base solvent, such as an ether, and to add a solution oforganomagnesium composition in ether to this slurry. The addition oforganomagnesium/ether solution to ether or co-solvent/carrier slurryusually takes place as a gradual continuous dropwise addition while theliquid medium of the slurry is maintained under reflux conditions.Without wishing to be bound by any operability theory, it is thoughtthat, upon such addition, dissolved organomagnesium composition mayreact with the carrier at the site of reactive OH groups, if any,present on the available surface area of the carrier. Such a reactionmay be described for ethylmagnesium chloride as follows:

    CARRIER-OH+C.sub.2 H.sub.5 MgCl→CARRIER-OMgCl+C.sub.2 H.sub.6

Accordingly, it may be possible to incorporate an organomagnesiumcomposition onto a carrier by reacting an organomagnesium compositionwith reactive OH groups of the carrier.

Another means of incorporating a magnesium composition onto a carrier isto precipitate a magnesium compound or compounds from an organomagnesiumcomposition from a liquid solvent onto a carrier. This precipitation maytake place by any possible convenient means, including cooling of thesolvent, using a sufficiently large amount of non-solvent in the initialslurry to precipitate the magnesium compound(s) within the carrier,adding non-solvent to the slurry to cause the precipitation of themagnesium compound(s) within the carrier, or stripping of solvent. Inthe case of a carrier slurry where the liquid solvent is essentially ahexane/tetrahydrofuran solution of ethylmagnesium chloride, it ispreferred to precipitate ethylmagnesium chloride onto the carrier bydistillation of the solvent. In this regard, it is noted thattetrahydrofuran and hexane have nearly equivalent boiling points. Thus,it would be expected that during the course of distilling thesesolvents, the ratio of tetrahydrofuran to hexane in the liquid statewould remain substantially constant. On the other hand, if the boilingpoint of the co-solvent is significantly greater than the boiling pointof the ether, then the relative concentration of the co-solvent mayincrease appreciably as the distillation proceeds. In such a case, anon-uniform precipitation of a magnesium compound may occur, such thatany magnesium halide, e.g., magnesium dihalide, which may be presenttends to precipitate before organomagnesium is precipitated.

In view of the above discussion, it will be understood that at leastthree possible types of magnesium-containing compounds on the carriercan be obtained. The first type is essentially one or more reactionproduct of an organomagnesium composition with a carrier having OHfunctionalities (i.e., OH groups) which are reactive with theorganomagnesium composition. This product contains substantially noprecipitated magnesium compound(s). Examples of such reaction productsare given in the aforementioned Stevens et al., U.S. Pat. No. 3,787,384and Strobel et al., U.S. Pat. No. 4,148,754.

A second type of product is substantially one or more magnesium compoundwhich is incorporated onto the carrier by means other than thosementioned above, i.e., it is not a reaction product of anorganomagnesium composition with a carrier having reactive OHfunctionalities. This product contains substantially no reaction productof an organomagnesium composition with the carrier. Such a product isobtained when an organomagnesium composition is precipitated onto acarrier having essentially no OH functionalities reactive with theorganomagnesium composition.

A third type of product contains both, one or more reaction product(s)of an organomagnesium composition with the carrier and precipitatedorganomagnesium composition(s). Such a product is obtained when anexcess of organomagnesium composition, with respect to the OHfunctionalities, is reacted with a carrier containing such reactive OHfunctionalities.

Accordingly, at least one magnesium-containing compound may beincorporated onto a carrier in either an unreacted form or in a reactedform or a combination of both forms. Without wishing to be bound by anytheory of operability, it is believed that the reactive form of themagnesium-containing compound is obtained by the reaction of reactivehydroxyl groups of the carrier with an organomagnesium composition.However, regardless of the possible mechanism of incorporating themagnesium-containing compound onto the carrier, it is important for thepurposes of the present invention that the number of moles of theorganomagnesium composition in the solution used to contact the carrieris in excess of the number of moles of OH groups on the carrier, so thatthe molar ratio of the organomagnesium composition in the solution tothe hydroxyl groups is greater tnan 1.0, preferably it is from about 1.1to about 3.5, and most preferably from about 2.0 to about 3.5.

It is also important for the purposes of the present invention, that thenumber of moles of the sum of all magnesium-containing compounds on thecarrier, in the product of the third step, designated above as step(iii), of the synthesis of the catalyst of this invention, is in excessof the number of moles of OH groups present on the carrier after theheating step (i) is completed. The molar ratio of the sum of allmagnesium-containing compounds in the product of the third step to theaforementioned OH groups is greater than 1, preferably it is from about1.1 to about 3.5 and most preferably from about 2.0 to about 3.5.

To assure that most, if not all, of the magnesium-containing compound(s)are retained on the carrier, the liquid is removed from the reactionvessel with care to assure that none or very little magnesium-containingcompound(s) are removed with it. The liquid may be removed by any meansassuring that substantially all of the magnesium-containing compound(s)remain on the carrier, e.g., by distillation of the mixture of theimpregnated carrier and the solvents, evaporation, decantation orcentrifugation. Evaporation at about the boiling point of the liquid isthe most preferred method of liquid removal. It is also important thatthe product of the third reaction step is not washed so that the excessof the magnesium-containing compound or compounds, which did not reactwith the hydroxyl (OH) groups of the carrier, is retained on thecarrier. After the liquid is removed, the resulting product is dried byany conventional means, e.g., drying at ambient temperature or at50°-80° C. for about 12-16 hours with a stream of dry nitrogen toproduce a free-flowing powder.

Whether the magnesium-containing compounds are in the form of a reactionproduct with the carrier or in the form of a non-reacted precipitate, itis noted that the magnesium-containing compounds may, optionally, be inthe form of a complex with one or more electron donating agents (i.e.,Lewis bases). For example, when ethylmagnesium chloride is precipitatedfrom a hexane/tetrahydrofuran solution, each mole of the ethylmagnesiumchloride precipitated may be complexed with approximately one mole oftetrahydrofuran. In more general terms, when an organomagnesiumcomposition is precipitated from a solution containing an ether, theresulting precipitate may have molecules of this ether complexed withmolecules of the organomagnesium composition.

The amount of magnesium-containing compound(s) which is incorporatedonto the carrier should be sufficient to react with the transition metalcompound in order to incorporate a catalytically effective amount of thetransition metal on the carrier in the manner set forth hereinbelow.Thus, the carrier should comprise from about 0.1 to about 50, preferablyabout 0.1 to about 5 millimoles (mmoles) of magnesium per gram ofcarrier (after the treatment of the carrier with the organomagnesiumcomposition is completed). When the first liquid containing anorganomagnesium composition is contacted with a carrier, the amount ofmagnesium in this liquid in terms of mmoles may be essentially the sameas that stated above which is incorporated onto the carrier.

When a non-Lewis base co-solvent is used to slurry the carrier, anamount of such co-solvent sufficient to slurry such a carrier is used,e.g., from about 2 to about 100 milliliters (mls), preferably from about5 to about 15 mls, of such co-solvent may be present per gram ofcarrier.

While the above-exemplified methods of incorporating a solid reactiveorganomagnesium composition onto a carrier are preferred, it will beunderstood that alternative methods are available. For instance, it ispossible to precipitate a dialkylmagnesium composition onto a carrierfrom a hydrocarbyl or halohydrocarbyl solvent containing essentially noether. It is also possible to combine a carrier and a solidorganomagnesium composition in the absence of a solvent by means of aball milling device. However, the use of such a ball milling device isnot desiraole, particularly because it does not tend to effectivelyincorporate a reactive magnesium compound into the pores of the carrier.

Mechanical shearing means, such as ball milling, are not necessary toachieve the desired manner of incorporation of the catalyst onto thecarrier in accordance with the present invention. Accordingly, a ballmilling process, such as that described in Examples 2-5 of Grant, U.S.Pat. No. 3,821,186, is unnecessary and should be avoided. Moreover, aball milling process may tend to disrupt the particle size andmorphology of the carrier. Since catalysts made in accordance with thepresent invention are capable of being used in gas phase, fluid bedpolymerization processes, e.g., as described by Karol et al. U.S. Pat.No. 4,302,566, the particle size and morphology of the catalyst may becritical. Accordingly, another reason for avoiding ball milling is topreserve the particle size and morphology of the carrier while it isbeing treated in accordance with the process of the present invention.

The free-flowing powder obtained in the third step of the catalystsynthesis process is reacted with at least one transition metal compounddissolved in a second liquid, also referred to herein as a liquid mediumdiluent. Suitable transition metal compounds are titanium, e.g.,tetravalent titanium compounds, such as TiCl₄, and vanadium, e.g.,tetravalent vanadium compounds. In the most preferred embodiment of thisinvention, one or more tetravalent titanium compound is the transitionmetal compound used in step (iv) of the catalyst synthesis process.

Since the catalyst synthesis and activation conditions for allembodiments of the invention are identical, for the sake ofsimplification, the invention will be described below in detail onlywith respect to the embodiment utilizing, in step (iv) of the catalystsynthesis process, the most preferred transition metal compound, i.e., atetravalent titanium compound. It will be understood by those skilled inthe art, however, that process and reaction conditions described belowfor that emoodiment can be applied to all other embodiments of theinvention.

The tetravalent titanium compound is soluble in the second liquid, whilethe treated carrier (i.e., the free-flowing powder), including themagnesium-containing compound(s), is insoluble therein. Thus, thereaction which takes place between the tetravalent titanium and thereactive magnesium-containing compound(s) is a reaction of a solid witha liquid. It is further noted that the reacted titanium is insoluble inthe liquid reaction medium.

Without wishing to be bound by any theory of operability, it is thoughtthat the reaction which takes place between (a) the magnesium compoundwhich is not a reaction product of an organomagnesium composition with acarrier and (b) the tetravalent titanium in the liquid reaction mediumis essentially an oxidation/reduction reaction, wherein the magnesiumcompound acts as a reducing agent for the tetravalent titanium. On theother hand, while not wishing to be bound by any particular theory orchemical mechanism, the reaction which takes place between (1)tetravalent titanium and (2) the reaction product of an organomagnesiumcomposition and the carrier containing reactive OH groups is not anoxidation/reduction reaction. However, it is noted that both of theabove-mentioned reactions lead to the incorporation of titanium onto thecarrier.

The tetravalent titanium compound or compounds which can be used are anytitanium compounds soluble in the liquid medium used in the fourth (iv)catalyst synthesis step, such as, titanium halides, e.g., titaniumtetrachloride, TiCl₄, titanium tetrabromide, TiBr₄, titanium alkoxides,wherein the alkoxide moiety has a branched or unbranched alkyl radicalof 1 to about 20 carbon atoms, preferably 1 to about 6 carbon atoms. Themost preferred titanium compound is titanium tetrachloride.

Mixtures of such titanium compounds may also be used and generally norestrictions are imposed on the titanium compounds which may beincluded. Any titanium compound that may be used alone may also be usedin conjunction with other titanium compounds.

Suitable liquid medium diluents are materials in which the tetravalenttitanium compounds are at least partially soluble and which are liquidat reaction temperatures. Preferred diluents are alkanes, such ashexane, n-heptane, octane, nonane, and decane, although a variety ofother materials including cycloalkanes, such as cyclohexane, aromatics,such as benzene and ethyloenzene, and halogenated and hydrogenatedaromatics, such as chlorobenzene, ortho-dichlorobenzene, can also beemployed. The most preferred diluent is n-heptane. Prior to use, thediluent should be purified, such as by percolation through silica geland/or molecular sieves, to remove traces of water, oxygen, polarcompounds, and other materials capable of adversely affecting catalystactivity. The magnesium-containing dry, free-flowing powder is reactedwith the tetravalent titanium compound at a temperature and for a timesufficient to yield a solid catalyst component (also referred to hereinas a catalyst precursor). Temperatures at which this reaction isconducted range from about -40° to about 250° C., preferably, from about0° to about 170° C., and most preferably, the reaction is conducted at atemperature of 25°-100° C. Suitable reaction times range from about 1/2to about 25 hours, with about 1/2 to about 6 hours being preferred.

The reaction of the tetravalent titanium in the liquid medium with themagnesium-containing carrier material conveniently takes place byslurrying the solid carrier in a solution of the tetravalent titaniumcompound in the diluent and heating the liquid reaction medium to asuitable reaction temperature, e.g., to the reflux temperature of thediluent at standard atmospheric pressure. Thus, the reaction may takeplace under reflux conditions.

The various reaction parameters can be widely varied, suitable selectionof such parameters being well within the skill of those having ordinaryskill in the art. The volume of the tetravalent titanium compoundsolution added to the magnesium-containing powder initially slurried inthe solution may be from about 0.1 to about 10 millimeters (mls) pergram of such carrier. The concentration of the titanium compoundsolution may be, for example, from about 0.1 to about 5 Molar. It isimportant, however, that the molar amount of the tetravalent titaniumcompound in the solution is in excess of the molar amount of theorganomagnesium composition used to treat the carrier in the first stepof the catalyst sythesis. Thus, the molar ratio of the tetravalenttitanium to the organomagnesium composition is from about 1 to about 10,preferably from about 3 to about 6. Unreacted titanium may be removed byany suitable separation techniques, such as decantation, filtrationand/or washing.

After the reaction is completed, the slurry, formed by the reactionmixture, is filtered, washed with a suitable washing agent, e.g., analkane, such as hexane, and dried in an inert atmosphere, e.g.,nitrogen. The thus-obtained catalyst precursor is then combined with acatalyst activator, in the manner and proportions discussed above, toform an active catalyst composition.

Steps (ii) through (iv) of the catalyst synthesis process of the presentinvention, and the step of combining the catalyst precursor with acatalyst activator, are conducted substantially in the absence of water,oxygen, and other catalyst poisons. Such catalyst poisons can beexcluded during the aforementioned catalyst preparation steps by anywell-known methods, e.g., by carrying out the preparation under anatmosphere of nitrogen, argon or other inert gas. An inert gas purge canserve the dual purpose of excluding external contaminants during thepreparation and removing undesirable reaction by-products resulting fromthe preparation of the neat, liquid reaction product. Purification ofany diluent employed in the third and fourth preparative steps in themanner described above also is helpful in this regard.

It may also be possible to replace some or all of the above-mentionedtetravalent titanium compounds with one or more other transition metalcompounds. Such other transition metal compounds are exemplified inGraff et al., U.S. Pat. No. 4,173,547, column 6, lines 55-60. Preferredreplacing transition metal compounds include zirconium compounds (e.g.,ZrCl₄.

The catalyst precursor obtained in step (iv) of the catalyst synthesismethod is then combined with a catalyst activator, also known as acatalyst promoter. The catalyst activator or promoter used herein is anyone of the well known polymerization catalyst activators. The activatorsinclude any of the materials commonly employed for such purpose forolefin polymerization catalyst components containing compounds of theGroup IVA, VA or VIA metals (as defined in the Periodic Chart of tneElements, published by Fisher Scientific Company, Catalog Number5-702-10). Examples of the promoters include Group IB, IIA, IIB, IIIBand IVB metal alkyls, hydrides, alkylhydrides, and alxylhalides, such asalkyllithium compounds, dialkylzinc compounds, trialkylboron compounds,trialkylaluminum compounds, alkylaluminum halides and hydrides, andtetraalkylgermanium compounds. Mixtures of activators can also beemployed. Specific examples of useful promoters include n-butyllithium,dietnylzinc, di-n-propylzinc, triethylboron, triethylaluminum,triisobutylaluminum, tri-n-hexylaluminum, ethylaluminum dichloride,dibromide, and dihydride, isobutyl aluminum dichloride, dibromide, anddihydride, diethylaluminum chloride, bromide, and hydride,di-n-propylaluminum chloride, bromide, and hydride, diisobutylaluminumchloride, bromide, and hydride, tetramethylgermanium, andtetraethylgermanium. Organometallic promoters which are preferably usedin accordance with this invention are the Group IIIB metal alkyls anddialkylhalides and trialkylhalides having 1 to about 20 carbon atoms peralkyl radical More preferably, the promoter is a trialkylaluminumcompound having 1 to about 6 carbon atoms per alkyl radical. The mostpreferred promoter is triethylaluminum (TEAL.)

The catalyst may be activated in situ by adding the activator andcatalyst separately to the polymerization medium. It is also possible tocombine tne catalyst and activator before the introduction thereof intothe polymerization medium, e.g., for up to about 2 hours at atemperature of from about -40° to about 80° C. In a preferredembodiment, the activator is introduced into a fluidized bedpolymerization process reactor simultaneously with, but separately from,the catalyst precursor an active polymerization catalyst composition.Normally, the ratio of the promoter to the precursor, either in a slurryor in a fluidized bed reaction process is about 0.3 to 1.5, depending onethylene partial pressure in the reactor and other variables.

Catalysts of the present invention exhibit high levels of productivityand excellent stability.

Alpha-olefins are preferably polymerized with the catalysts preparedaccording to the present invention in gas phase polymerizationreactions, e.g., those taking place in stirred bed reactors and,especially, fluidized bed reactors.

The molecular weight of the polymer may be controlled in a known manner,e.g., by using hydrogen. With the catalysts produced according to thepresent invention, molecular weight may be suitably controlled withhydrogen when the polymerization is carried out at relatively lowtemperatures, e.g., from about 30° to about 105° C. This control ofmolecular weight may be evidenced by a measurable positive melt index ofthe polymer produced.

The molecular weight distribution of the polymers prepared in thepresence of the catalysts of the present invention, as measured by themelt flow ratio (MFR) values, varies from about 26 to about 50 for HDPEproducts having a density of about 0.945 to about 0.960, and a I₂ meltindex of about 0.1 to about 100, and from about 28 to about 50 for LLDPEproducts having a density of about 0.915 to about 0.940, and an I₂ meltindex of about 0.1 to about 100. As is known to those skilled in theart, higher MFR values are indicative of a relatively broad molecularweight distribution of the polymer.

The catalysts prepared according to the present invention are highlyactive and may have an activity of at least about 500-7,000 grams ofpolymer per gram of catalyst per 100 psi of ethylene in about 3 hours.

Advantageous properties of linear low density polyethylene polymers aredescribed by Anderson et al, U.S. Pat. No. 4,076,698. The linear lowdensity polyethylene polymers prepared in accordance with the presentinvention are polymers of ethylene alone and preferably copolymers ofethylene with one or more C₃ -C₁₀ alpha-olefins. Thus, copolymers havingtwo monomeric units are possible as well as terpolymers having threemonomeric units. Particular examples of such polymers includeethylene/1-butene copolymers, ethylene/1-hexene copolymers,ethylene/4-methyl-1-pentene copolymers, ethylene/1-butene/1-hexeneterpolymers, ethylene/propylene/1-hexene terpolymers andethylene/propylene/1-butene terpolymers. When propylene is employed as acomonomer, the resulting linear low density polyethylene polymerpreferably has at least one other alpha-olefin comonomer having at leastfour carbon atoms in an amount of at least 1 percent by weight of thepolymer. Accordingly, ethylene/propylene copolymers are possible, butnot preferred. The most preferred polymer is a copolymer of ethylene and1-hexene.

The linear low density polyethylene polymers produced in accordance withthe present invention preferably contain at least about 80 percent byweight of ethylene units.

A particularly desirable method for producing linear low densitypolyethylene polymers according to the present invention is in a fluidbed reactor. Such a reactor and means for operating same is described byLevine et al., U.S. Pat. No. 4,011,382 and Karol et al., U.S. Pat. No.4,302,566, the entire contents of both of which are incorporated hereinby reference.

A preferred process for conducting a gas phase, fluid bed polymerizationis described below.

The polymerization reaction is conducted by contacting a stream of themonomers, in a gas phase process, such as in the fluid bed processdescribed below, and substantially in the absence of catalyst poisons,such as moisture, oxygen, CO, CO₂, and acetylene, with a catalyticallyeffective amount of the completely activated catalyst at a temperatureand at a pressure sufficient to initiate the polymerization reaction.

In order to achieve the desired density ranges in the copolymers, it isnecessary to copolymerize a sufficient amount of the comonomers havingthree or more carbon atoms with ethylene to achieve a level of 0 toabout 20 mol percent of the C₃ to C₈ comonomer in the copolymer. Theamount of comonomer needed to achieve this result depends on theparticular comonomer(s) employed.

Thus, 1-hexene can be incorporated into an ethylene polymer chain in agas phase reactor in amounts up to 20 percent by weight, preferablyabout 5 to about 12 percent by weight. The reaction is preferablyconducted in a fluid bed reactor using the catalyst of the invention.

A fluidized bed reaction system which can be used in the process of thepresent invention is illustrated in FIG. 1. With reference thereto, areactor 10 consists of a reaction zone 12 and a velocity reduction zone14.

The reaction zone 12 comprises a bed of growing polymer particles,formed polymer particles and a minor amount of catalyst particlesfluidized by the continuous flow of polymerizable and modifying gaseouscomponents in the form of make-up feed and recycle gas through thereaction zone. To maintain a viable fluidized bed, the mass gas flowrate through the bed must be above the minimum flow required forfluidization, and preferably from about 1.5 to about 10 times G_(mf) andmore preferably from about 3 to about 6 times G_(mf). The term G_(mf) isused herein in the accepted form as the abbreviation for the minimummass gas flow required to achieve fluidization, see C. Y. Wen and Y. H.Yu, "Mechanics of Fluidization", Chemical Engineering Progress SymposiumSeries, Vol. 62, p. 100-111 (1966).

It is essential that the bed always contains polymer particles toprevent the formation of localized "hot spots" and to entrap anddistribute the particulate catalyst throughout the reaction zone. Onstart up, the reaction zone is usually charged with a base ofparticulate polymer particles before gas flow is initiated. Suchparticles may be identical in nature to the polymer to be formed ordifferent therefrom. When they are different, they are withdrawn withthe desired formed polymer particles as the first product. Eventually, afluidized bed of the desired polymer particles supplants the start-upbed.

The partially or completely activated catalyst used in the fluidized bedis preferably stored for service in a reservoir 32 under a blanket of agas which is inert to the stored material, such as nitrogen or argon.

Fluidization is achieved by a high rate of gas recycle to and throughthe bed, typically on the order of about 50 times the rate of feed ofmake-up gas. The fluidized bed has the general appearance of a densemass of viable particles in possible free-vortex flow as created by thepercolation of gas through the bed. The pressure drop through the bed isequal to or slightly greater than the weight of the bed divided by thecross-sectional area. It is thus dependent on the geometry of thereactor.

Make-up gas is fed to the bed at a rate equal to the rate at whichparticulate polymer product is withdrawn. The composition of the make-upgas is determined by a gas analyzer 16 positioned above the bed. The gasanalyzer determines the composition of the gas being recycled and thecomposition of the make-up gas is adjusted accordingly to maintain anessentially steady state gaseous composition within the reaction zone.

To ensure complete fluidization, the recycle gas and, where desired,part of the make-up gas are returned to the reactor at point 18 belowthe bed. A gas distribution plate 20 is positioned above the point ofreturn to aid fluidization of the bed.

The portion of the gas stream which does not react in the bedconstitutes the recycle gas which is removed from the polymerizationzone, preferably by passing it into a velocity reduction zone 14 abovethe bed where entrained particles are given an opportunity to return tothe bed. Particle return may be aided by a cyclone 22 which may be partof the velocity reduction zone or exterior thereto. Where desired, therecycle gas may then be passed through a filter 24 designed to removesmall particles at high gas flow rates to prevent dust from contactingheat transfer surfaces and compressor blades.

Tne recycle gas is then compressed in a compressor 25 and then passedthrough a heat exchanger 26 wherein it is stripped of heat of reactionbefore it is returned to the bed. By constantly removing heat ofreaction, no noticeable temperature gradient appears to exist within theupper portion of the bed. A temperature gradient will exist in thebottom of the bed in a layer of about 6 to 12 inches, between thetemperature of the inlet gas and the temperature of the remainder of thebed. Thus, it has been observed that the bed acts to almost immediatelyadjust the temperature of the recycle gas above this bottom layer of thebed zone to make it conform to the temperature of the remainder of thebed, thereby maintaining itself at an essentially constant temperatureunder steady state conditions. The recyc-e gas is then returned to thereactor at its base 18 and to the fluidized bed through a distrioutionplate 20. The compressor 25 can also be placed upstream of the heatexchanger 26.

The distribution plate 20 plays an important role in the operation ofthe reactor. The fluidized bed contains growing and formed particulatepolymer particles as well as catalyst particles. As the polymerparticles are hot and possibly active, they must be prevented fromsettling, for if a quiescent mass is allowed to exist, any activecatalyst contained tnerein may continue to react and cause fusion.Diffusing recycle gas through the bed at a rate sufficient to maintainfluidization at the base of the bed is, therefore, important. Thedistribution plate 20 serves this purpose and may be a screen, slottedplate, perforated plate, a plate of the bubble cap type, or any similarplate known in the art. The elements of tne plate may all be stationary,or the plate may be of the mobile type disclosed in U.S. Pat. No.3,298,792, the entire contents of which are incorporated herein byreference. Whatever the design of the plate, it must diffuse the recyclegas through the particles at the base of the bed to keep them in afluidized condition, and also serve to support a quiescent bed of resinparticles when the reactor is not in operation. The mobile elements ofthe plate may be used to dislodge any polymer particles entrapped in oron the plate.

Hydrogen may be used as a chain transfer agent in the polymerizationreaction of the present invention. The ratio hydrogen/ethylene employedvaries between about 0 to about 2.0 moles of hydrogen per mole of theethylene monomer in the gas stream.

Any gas inert to the catalyst and reactants can also be present in thegas stream. The activator compound is preferably added to the reactionsystem at the hottest portion of the gas which is usually downstreamfrom heat exchanger 26. Thus, the activator may be fed into the gasrecycle system from dispenser 27 through line 27A. As discussed above,the rate of feed of the activator compound, for a given desired contentof the activator compound in the polymer product, is a function of therate of product polymer production. The rate of the polymer productionis controlled by the timer controlling two timed valves 36 and 38, asdiscussed in detail below.

Zinc (Zn) compounds of the structure Zn(R_(a))(R_(b)), wherein R_(a) andR_(b) are the same or different C₁ to C₁₄ aliphatic or aromatichydrocarbon radicals, may be used in conjunction with hydrogen, with tnecatalysts of the present invention as molecular weight control or chaintransfer agents, that is, to increase the melt flow index values of thecopolymers that are produced. About 0 to 50, and preferably about 20 to30, moles of the Zn compound (as Zn) may optionally be used in the gasstream in the reactor per mole of titanium compound in the reactor. Thezinc compounds are introduced into the reactor preferably in the form ofa dilute solution (2 to 30 weight percent) in hydrocarbon solvent orabsorbed on a solid diluent material, such as silica, of the typesdescribed above, in amounts of about 10 to about 50 weight percent.These compositions tend to be pyrophoric. The zinc compound may be addedalone, or with any additional portions of the activator compound thatare to be added to the reactor from a feeder, not shown, which could bepositioned adjacent dispenser 27, near the hottest portion of the gasrecycle system.

It is essential to operate the fluid bed reactor at a temperature belowthe sintering temperature of the polymer particles. To ensure thatsintering will not occur, operating temperatures below the sinteringtemperature are desired. For the production of ethylene/1-hexenecopolymers in the process of the present invention an operatingtemperature of about 30° to 115° C. is preferred, and a temperature ofabout 75° to 95° C. is most preferred. Temperatures of about 75° to 90°C. are used to prepare polymer products having a density of about 0.90to 0.93 gms/cc, temperatures of about 85° to 100° C. are used to prepareproducts having a density of about 0.92 to 0.95 gms/cc, and temperaturesof about 90° to 115° C. are used to prepare products having a density ofabout 0.94 to 0.96 gms/cc.

The fluid bed reactor is operated at pressures of up to about 1000 psi,and is preferably operated at a pressure of from about 150 to 350 psi,with operation at the higher pressures in such ranges favoring heattransfer since an increase in pressure increases the unit volume heatcapacity of the gas.

The partially or completely activated catalyst is injected into the bedat a rate equal to its consumption at a point 30, which is above thedistribution plate 20. Injecting the catalyst at a point above thedistribution plate is an important feature of the process of thisinvention. Since the catalysts used in the practice of this inventionare highly active, injection of the fully activated catalyst into thearea below the distribution plate may cause polymerization to begin inthat area and eventually cause plugging of the distribution plate.Injection into the viable bed, instead, aids in distributing thecatalyst throughout the bed and tends to preclude the formation oflocalized spots of high catalyst concentration which may result in theformation of "hot spots".

A gas which is inert to the catalyst, such as nitrogen or argon, is usedto carry the partially or completely reduced precursor composition intothe bed.

The production rate of the bed is controlled by the rate of catalystinjection. The production rate may be increased by simply increasing therate of catalyst injection and decreased by reducing the rate ofcatalyst injection.

Since any change in the rate of catalyst injection will change the rateof generation of the heat of reaction, the temperature of the recyclegas is adjusted upwards or downwards to accommodate the change in therate of heat generation. This ensures the maintenance of an essentiallyconstant temperature in the bed. It will be apparent to those skilled inthe art that complete instrumentation of both the fluidized bed and therecycle gas cooling system is necessary to detect any temperature changein the bed to provide a means for a suitable adjustment in thetemperature of the recycle gas.

Under a given set of operating conditions, the fluidized bed ismaintained at essentially a constant height by withdrawing a portion ofthe bed as product at a rate equal to the rate of formation of theparticulate polymer product. Since the rate of heat generation isdirectly related to product formation, a measurement of the temperaturerise of the gas across the reactor (the difference between inlet gastemperature and exit gas temperature) is determinative of the rate ofparticulate polymer formation at a constant gas velocity.

The particulate polymer product is preferably continuously withdrawn ata point 34 at or close to the distribution plate 20 and in suspensionwith a portion of the gas stream which is vented before the particulatessettle to preclude further polymerization and sintering when theparticles reach their ultimate collection zone. The suspending gas mayalso be used to drive the product of one reactor to another reactor.

The particulate polymer product is conveniently and preferably withdrawnthrough the sequential operation of a pair of timed valves 36 and 38defining a segregation zone 40. While valve 38 is closed, valve 36 isopened to emit a plug of gas and product to the zone 40 between it andvalve 36 which is then closed. Valve 38 is then opened to deliver theproduct to an external recovery zone. Valve 38 is then closed to awaitthe next product recovery operation.

Finally, the fluidized bed reactor is equipped with an adequate ventingsystem to allow venting the bed during start up and shut down. Tnereactor does not require the use of stirring means and/or wall scrapingmeans.

The highly active supported catalyst system of this invention yields afluid bed product having a geometric mean particle size between about0.005 to about 0.07 inches and preferably about 0.02 to about 0.05inches.

The feed stream of a gaseous monomer, with or without inert gaseousdiluents, is fed into the reactor at a space time rate of about 2 to 10pounds/hour/cubic foot of bed volume.

The term virgin resin or polymer as used herein means polymer, ingranular form, as it is recovered from the polymerization reactor.

Catalysts of the present invention are used to produce polymers havingthe desired combination of density and melt index by adjusting the gasphase partial pressure ratios in the reactor. Thus, e.g., the ratio of1-hexene to ethylene primarily controls the product density, and theratio of hydrogen to ethylene primarily controls the melt index. Thecatalysts of the present invention are particularly suitable for theproduction of polymers used in manufacturing low density films andinjection molding products.

The following Examples further illustrate the essential features of theinvention. However, it will be apparent to those skilled in the art thatthe specific reactants and reaction conditions used in the Examples areused only to illustrate the invention and are not intended to limit thescope thereof to the specific reactants and conditions illustrated inthe Examples.

EXAMPLE 1 (Comparative Catalyst Preparation)

All procedures were carried out in glass or quartz equipment underpurified nitrogen using pre-dried nitrogen-purged solvents.

Davison Silica Gel, Grade 952, was activated by fluidizing withnitrogen, heating at 800° C. for 9 hours and cooled to room temperatureunder nitrogen.

700 grams of the activated silica was introduced into a 10 litercone-bottomed glass reactor fitted with a stirrer, thermometer, additionnozzle, dry nitrogen line and a distillation head to remove solvent. Thereactor was contained in a water jacket maintained at a controlledtemperature.

7 liters of hexane was added to the silica while stirring under a slownitrogen purge. The silica/hexane slurry was brought to a refluxtemperature of 70° C. and 483 mls of a 2.0M solution of ethylmagnesiumchloride in tetrahydrofuran (THF) added slowly over a 4 minute period.The reflux was continued for an additional 60 minutes. The solvents wereremoved by distillation and the silica dried at approximately 80° C.under a nitrogen purge. This product was slurried with a pre-mixedsolution of 390 mls of TiCl₄ dissolved in 6.5 liters of n-heptane, andthe slurry refluxed for 2 hours, using the same apparatus as describedabove. The mixture was allowed to cool to room temperature. The solidswere then washed 2 times with 7 liter portions of hexane and 3 timeswith 7 liter portions of isopentane, and dried under a nitrogen purge.760 grams of catalyst precursor in the form of a free flowing tancolored powder was obtained. Analyses of the powder indicated that itcontained 1.0 mmols of Mg/gram of catalyst and 0.75 mmols of Ti/gram ofcatalyst. This precursor was then combined with triethylaluminum (TEAL)activator, as set forth below in Example 3.

EXAMPLE 2 (Preparation of Catalyst)

A catalyst of the present invention was synthesized by followingsubstantially the same preparative steps of Example 1, except that airwas used in heating Davison Silica Gel, Grade 952, at 800° C. for 9hours.

EXAMPLE 3 (Polymerization With Catalyst of Examples 1 and 2)

The catalysts of Examples 1 and 2 were used to polymerize ethylene and1-hexene in a continuous fluidized bed reactor. The reaction zonecontained approximately 50 kg of particulate resin in a volume of about220 liters. The bed was fluidized with a gas flow of 40 to 50 cm/sec.Bed temperature was maintained constant by controlling the temperatureof the fluidizing gas at the reactor inlet (designated by numeral 18 inFIG. 1).

The feed rate of ethylene was maintained constant for each experiment.The partial pressure of ethylene was controlled by adjustments in thecatalyst feed rate. Increases in the catalyst feed rate producedproportional increases in reaction rate which, for a fixed feed rate ofethylene, lowered the ethylene partial pressure. Decreases in thecatalyst feed rate produced higher ethylene partial pressures.

Gas phase partial pressure ratios of 1-hexene/ethylene andhydrogen/ethylene were continually monitored by a process gaschromatograph, and were controlled by adjustments in the feed ratio of1-hexene and hydrogen, respectively.

The catalyst precursor and the TEAL activator were introduced into thereactor through two separate inlet ports and the rate of theintroduction thereof was controlled independently. The TEAL feed ratewas determined by the desired level of TEAL in the polymer product(150-175 ppmw). The TEAL feed rate was adjusted as required to maintainan approximately constant ratio of TEAL feed to polymer production rate.

The polymerization conditions were identical for both catalysts, andthey are set forth below in Table 1.

                  TABLE 1                                                         ______________________________________                                        Reactor Conditions                                                            ______________________________________                                        Temperature            87° C.                                          Ethylene (C.sub.2.sup.=) Partial Pressure                                                            85 ± 3 psi                                          TEAL Feed              150-175 ppm                                            Resin Production Rate  22 ± 1 lbs/hr.                                      Catalyst Residence Time                                                                              4.9-5.2 hrs.                                           H.sub.2 /C.sub.2 Partial Pressure Ratio                                                              0.25-0.28                                              ______________________________________                                    

The hexene/ethylene (C₆ /C₂) gas phase partial pressure ratio wasadjusted as required to produce a polymer within the target 0.918-0.920gm/cc density range. Typical C₆ /C₂ values were 0.120-0.130.

The catalyst of Example 2, made with air-activated silica, gavesuprisingly high productivity as compared to that of Example 1 (5390 gmspolymer/gm of Example 2 catalyst, compared to 4150 gms polymer/gm ofExample 1 catalyst). Resin bulk density was also increased to 20.5pounds per cubic foot from 17.8 pounds per cubic foot.

EXAMPLE 4 (Controlled Synthesis of Catalyst)

Two more catalyst samples were prepared from the same batch of rawsilica to determine if different silica samples used in Examples 1 and 2had any effect on the catalyst properties.

One of the catalyst samples (Example 4A) was prepared with air-activatedsilica, while the other with nitrogen-activated silica (Example 4B).Both catalyst samples were prepared by a procedure substantially thesame as in Example 1.

Each of the catalyst samples had a nominal magnesium loading of 1.27mmoles per gram of dry silica. These catalysts were then tested understandardized reactor conditions of Table 1. The results, shown below inTable 2, confirmed that the air activation produced a catalyst withhigher productivity and bulk density than the nitrogen activation. Thefollowing table shows the combined results from four catalyst tests.

                  TABLE 2                                                         ______________________________________                                        Reaction Process Data                                                         Catalyst                                                                             Silica               Resin Bulk                                                                            C.sub.6 /C.sub.2 for                      of     Activated Productivity                                                                             Density 0.918 gr/cm.sup.3                         Example                                                                              by        (gr/gr)    (lbs/ft.sup.3)                                                                        density                                   ______________________________________                                        1      N.sub.2   4150       17.8    0.133                                     .sup. 4B                                                                             N.sub.2   4450       19.4    0.123                                     2      Air       5390       20.5    0.124                                     .sup.  4A                                                                            Air       6330       20.0    0.129                                     Average                                                                              N.sub.2   4300       18.6    0.128                                     Average                                                                              Air       5860       20.7    0.127                                     ______________________________________                                    

The average productivity of the air activated catalysts was 36% higherthan that of their nitrogen equivalents. Bulk density was higher by anaverage of 11%.

Other important variables in the reaction process include comonomerincorporation and TEAL response. Comonomer incorporation is a measure ofthe ability of the catalyst to incorporate hexene or other comonomerinto the polymer chains. Catalysts with improved incorporation requirelower C₆ /C₂ gas phase ratios to reach a given (low) value of density.Table 2 shows the C₆ /C₂ ratio required to reach 0.918 gr/cm³ density at2 melt index (MI₂). The indicated values range from 0.123 to 0.133.Experimental error for these measurements is ±6% (three standarddeviations). Within this range of confidence, there is no differenceindicated between the catalysts prepared with air and nitrogen-activatedsilica (0.127 average air vs. 0.128 average N₂).

TEAL response of the catalysts made with air-activated silica was nottested directly, but qualitatively the response seemed to be similar tothat of the conventional catalysts of this type. With higher TEAL feeds,the productivity decreased, slightly as expected.

Resin samples from each of the four catalyst tests were analyzed forfilm strength and other important product properties.

The resin samples had densities between 0.918 and 0.920 gm/cc, and highload melt index (HLMI) values between 50 and 76. Product melt flow ratio(MFR) was essentially equal in all samples (34.3-36.2), indicating nodifference between catalysts prepared with air and N₂ activated silicain this respect.

Film strength was measured in Elmendorf Machine Direction (MD) andTransverse Direction (TD) tear, and Spencer impact tests. Multipledeterminations were made for each sample. Table 3 shows the measuredaverage values and standard deviations. Within experimental error, thereis no apparent difference in film strength between catalysts preparedwith air and nitrogen activated silica.

                                      TABLE 3                                     __________________________________________________________________________    Film Strength Properties                                                            Silica          Melt Index.sup.(A)                                      Catalyst                                                                            Activation                                                                          No. of                                                                             Density                                                                            (MI.sub.21)                                                                          MFR.sup.(B)                                                                         MD Tear.sup.(C)                                                                     TD Tear.sup.(C)                                                                     Spencer Impact.sup.(C)         of Example                                                                          by    Samples                                                                            (gm/cc)                                                                            (gm/10 min.)                                                                         (MI.sub.21 /MI.sub.2)                                                               (gm/mil)                                                                            (gm/mil)                                                                            (gm/mil)                       __________________________________________________________________________    1     N.sub.2                                                                             1    0.918                                                                              76.4   34.3  260 ± 52                                                                         543 ± 54                                                                          584 ± 116                  .sup. 4B                                                                            N.sub.2                                                                             3    0.920                                                                              50.5   36.2  226 ± 26                                                                         605 ± 35                                                                         736 ± 85                    2     Air   5    0.919                                                                              73.9   35.1  206 ± 18                                                                         560 ± 25                                                                         637 ± 57                    .sup. Air   3    0.919                                                                              65.2   34.7  237 ± 27                                                                         542 ± 31                                                                         696 ± 80                    Average                                                                             N.sub.2    0.919                                                                              63.5   35.2  243 ± 24                                                                         574 ± 29                                                                         660 ± 66                    Average                                                                             Air        0.919                                                                              69.6   34.9  222 ± 16                                                                         551 ± 19                                                                         667 ± 47                    __________________________________________________________________________     .sup.(A) MI.sub.21 ASTM D1238 Condition F                                     .sup.(B) MFR is the ratio MI.sub.21 /MI.sub.2, ASTM D1238, Condition          F/Condition E                                                                 .sup.(C) ± Range represents 95% confidence limits based on number of       samples and typical standard deviations.                                 

The results indicate that air activation of the silica improves thecatalyst productivity and bulk density without impairment of otherproperties. The higher productivity allows the polymerization reactor tooperate at lower ethylene partial pressure for improved monomerefficiency.

The increased bulk density gives a further improvement in monomerefficiency. For a given production rate from the reactor, the volume ofresin discharged per unit time is reduced. This lowers the associatedloss of ethylene and comonomer from the product discharge systems.

The higher bulk density also allows a small (1° C.) increase in safereactor operating temperature because of the higher mass of resin in thefluid bed available to absorb heat of reaction. The higher temperatureenables a 3-4% increase in maximum, heat transfer limited, productionrate from the reactor.

EXAMPLE 5 (Controlled Synthesis of Catalyst)

Two more catalyst samples were prepared with a different type ofsilica--Davison 955--than that used in the synthesis of the catalysts ofExamples 1, 2 and 4. The same batch of raw silica was used to prepareboth catalyst samples.

One of the catalyst samples (Example 5A) was prepared with air-activatedsilica, while the other (Example 5B) with nitrogen activated silica.Both catalyst samples were prepared by a procedure substantially thesame as that of Example 1. They were subsequently used to polymerizeethylene and 1-hexene in a fluid bed reactor of Example 3 understandardized reactor operating conditions of Table 2. Table 4 shows thetest results.

                  TABLE 4                                                         ______________________________________                                        Catalyst                                                                             Silica               Resin Bulk                                                                            C.sub.6 /C.sub.2 for                      of     Activated Productivity                                                                             Density 0.918 gr/cm.sup.3                         Example                                                                              by        (gr/gr)    (lbs/ft.sup.3)                                                                        density                                   ______________________________________                                        5A     Air       5940       23.7    0.141                                     5B     N.sub.2   4980       24.0    0.135                                     ______________________________________                                    

The results indicate that air activation of the Davison 955 silica alsoproduces alpha-olefin polymerization catalysts having increasedproductivity. The bulk density of the polymers prepared with thesespecific catalyst samples was substantially the same. Film strength andother product properties of the resin samples prepared with thecatalysts of Examples 5A and 5B were determined in the same manner asdescribed above in Example 4. The results, summarized in Table 5, below,indicate that, within experimental error, there is no apparentdifference in film strength between catalysts prepared with air andnitrogen activated silica.

                                      TABLE 5                                     __________________________________________________________________________    Film Strength Properties                                                            Silica          Melt Index.sup.(A)                                      Catalyst                                                                            Activation                                                                          No. of                                                                             Density                                                                            (MI.sub.21)                                                                          MFR.sup.(B)                                                                         MD Tear.sup.(C)                                                                     TD Tear.sup.(C)                                                                     Spencer Impact.sup.(C)         of Example                                                                          by    Samples                                                                            (gm/cc)                                                                            (gm/10 min.)                                                                         (MI.sub.21 /MI.sub.2)                                                               (gm/mil)                                                                            (gm/mil)                                                                            (gm/mil)                       __________________________________________________________________________    5A    air   3    0.918                                                                              53.6   33.3  289 ± 33                                                                         577 ± 33                                                                         817 ± 94                    5B    N.sub.2                                                                             2    0.919                                                                              56.2   32.8  264 ± 37                                                                         591 ± 42                                                                         685 ± 97                    __________________________________________________________________________     .sup.(A) MI.sub.21 ASTM D1238 Condition F                                     .sup.(B) MFR is the ratio MI.sub.21 /MI.sub.2, ASTM D1238, Condition          F/Condition E                                                                 .sup.(C) ± Range represents 95% confidence limits based on number of       samples and typical standard deviations.                                 

It will be apparent to those skilled in the art that the specificembodiments discussed above can be succesfully repeated with ingredientsequivalent to those generically or specifically set forth above andunder variable process conditions.

From the foregoing specification, one skilled in the art can readilyascertain the essential features of this invention and without departingfrom the spirit and scope thereof can adapt it to various diverseapplications.

What is claimed is:
 1. In a process for preparing a polymer of at leastone C₂ -C₁₀ alpha-olefin, the polymer containing at least about 80percent by weight of ethylene units, the process comprising conductingthe polymerization in the presence of a catalyst prepared by combining acatalyst precursor with at least one catalyst promoter, the catalystprecursor being prepared by a process comprising the steps of:(i)heating a solid, porous carrier having reactive OH groups; (ii)contacting the solid, porous carrier with a first liquid, said firstliquid containing at least one organomagnesium composition having theempirical formula

    R.sub.n MgR'.sub.(2-n)                                     (I)

where R and R' are the same or different and they are C₁ -C₁₂hydrocarbyl groups, provided that R' may also be a halogen, and n is 0,1 or 2, the number of moles of said organomagnesium composition being inexcess of the number of moles of said OH groups on said carrier; (iii)removing said first liquid from step (i) to obtain amagnesium-containing carrier in the form of a dry, free-flowing powder;and (iv) contacting said powder of step (iii) with a solution comprisinga second liquid and at least one transition metal compound, saidtransition metal compound being soluble in said second liquid, and saidmagnesium of said carrier being substantially insoluble in said secondliquid, whereby a compound of transition metal, which is insoluble insaid second liquid becomes incorporated onto said carrier;an improvementcomprising heating the solid, porous carrier in step (i) in theatmosphere of an oxygen-containing gas.
 2. A process of claim 1 whereina copolymer is prepared.
 3. A process of claim 2 wherein the copolymeris selected from the group consisting of ethylene/1-butene,ethylene/1-hexene, ethylene/4-methyl-1-pentene,ethylene/1-butene/1-hexane, ethylene/propylene/1-hexene andethylene/propylene/1-butene copolymers.
 4. A process of claim 3 whereinthe copolymer is a copolymer of ethylene and 1-hexene.
 5. A process ofclaim 4 wherein the oxygen-containing gas comprises at least 1% byvolume of oxygen.
 6. A process of claim 5 wherein the oxygen-containinggas comprises 15% to 50% by volume of oxygen.
 7. A process of claim 6wherein the oxygen-containing gas is ambient air comprising about 21% byvolume of oxygen.
 8. A process of claim 7 wherein the support is silicacomprising reactive OH groups.
 9. A process of claim 8 wherein silicacomprises about 0.1 to 2 mmoles of reactive OH groups per gram of silicaafter the heating step (i) is completed.
 10. A process of claim 9wherein the number of moles of said transition metal compound present insaid solution of step (iv) is in excess of the stoichiometric amountthereof.
 11. A process of claim 10 wherein the silica is heated at atemperature of about 800° C.
 12. A process of claim 11 wherein theheating is continued until the silica comprises about 0.3 to about 0.7mmoles of the OH groups per gram of carrier.
 13. A process of claim 12wherein the carrier is silica having a surface hydroxyl groupconcentration of about 0.5 mmoles/gr, a surface area of 300 M² /gram anda pore volume of 1.65 m³ /gram.
 14. A process of claim 13 wherein R is aC₁ -C₄ alkane group and R' is a halogen.
 15. A process of claim 14wherein R' is bromine or chlorine.
 16. A process of claim 15 wherein theorganomagnesium composition is ethylmagnesium chloride.
 17. A process ofclaim 16 wherein the first liquid is tetrahydrofuran.
 18. A process ofclaim 17 wherein the first liquid is removed in step (iii) byevaporation.
 19. A process of claim 18 wherein the molar ratio of theorganomagnesium composition to the number of moles of the OH groups onthe carrier is about 1.1 to about 3.5.
 20. A process of claim 19 whereinthe transition metal compound is a tetravalent titanium compound.
 21. Aprocess of claim 20 wherein the molar ratio of the tetravalent titaniumcompound to the organomagnesium composition is from about 3 to about 6.22. A process of claim 21 wherein the tetravalent titanium compound istitanium tetrachloride.
 23. A process of claim 22 wherein the catalystpromoter is at least one Group IIIB metal alkly, dialkylhalide ortrialkylhalide having 1 to 20 carbon atoms per alkyl radical.
 24. Aprocess of claim 23 wherein the catalyst promoter is a trialkylaluminumcompound having 1 to 6 carbon atoms per alkyl radical.
 25. A process ofclaim 24 wherein the catalyst promoter is triethylaluminum.
 26. Aprocess of claim 25 wherein the productivity of the process is increasedas compared to the same process conducted in the presence of thecatalyst prepared with the solid, porous carrier heated in theatmosphere of a substantially pure nitrogen gas.
 27. A process of claim26 wherein the productivity is increased by at least about 25%.
 28. Aprocess of claim 27 wherein the polymer product has a higher bulkdensity as compared to polymer products prepared in the presence ofsimilar catalysts prepared with the solid, porous carrier heated in theatmosphere of a substantially pure nitrogen gas.